[Terry Mross]

The Zero system brings it down to 0 ppm. But the filters cost about $15 each.

[justa-hairyape]

Have heard of sand filters being used to trap particulates. For example - The Scripps Institute Pier in La Jolla California has a filtration system where the public can get filtered seawater. But it is only sand filtered.

My PPM readings came from a handheld TDS meter (total dissolved solids). Think it measures conductivity. My RODI unit has a carbon prefilter and two particulate prefilters. If your filter can get 450-500 ppm down to 0 ppm, that has to be more then just sand.